Belveth isn't fun to play anymore. The champion is so overnerfed that every other skirmisher jungler beats you 1v1 at level 4 and has more damage for ganks. I swapped to the meta junglers, Shyvanna and Khazix and I immediately see better WR and easier games.

Belveth was released in 12.11 and received major nerfs on the following patches: 12.2, 12.21, 13.9, 13.20, 13.21, 14.5, 14.9 and 14.14. All of her skills have had multiple aspects of the skill nerfed, and as well, some of these aspects have been serially nerfed up to 4 times in a row

The exact patch notes are at the end, and I will summarize the major cumulative effects of the nerfs:

BASE STATS

Attack Range - 125-> 175 -> 150 (25 range added back to True Form as "compensation")

AD Growth - 2-> 1.7 -> 1.5

HP Growth - 105 ->99

Base health regeneration 8.5 -> 6

Health regeneration growth reduced 0.85 -> 0.6

PASSIVE - Bonus attack speed per Lavender stack 0.25%-1.25% -> 0.28%-1% (based on level)

PASSIVE - AS scaling until level 13 -> level 17 (takes longer to scale)

PASSIVE - Bonus attack speed from ability casts reduced 25%−50% (based on level) -> 20-50%

Q - AD ratio 110% ->100%

Q - Monster damage AD ratio - 120% -> 140% -> 120% -> 0% (when nerfed to 0, gave 45/55/65/75/85 bonus flat damage as "compensation")

E - Minimum base damage per hit reduced to 8 / 10 / 12 / 14 / 16 from 8 / 11 / 14 / 17 / 20

E - Life steal 20/22/24/26/28% -> 20/21.5/23/24.5/26% -> 20% all ranks

E - CD 22/20/18/16/14 -> 22/20.5/19/17.5/16 -> 24/22.5/21/19.5/18 -> 20/19/18/17/16

E - DR 70% all ranks ->42/49/56/63/70 -> 35/40/45/50/55% 

If you want a hilarious comparison, a lot of people on r/leagueoflegends and r/YIMO went apeshit over the following Yi change 14.12 to DR/CD that is a tiny fraction of what Belveth received:

Meditate (W)

• Cooldown increased to 10 seconds from 9.
• Initial damage reduction reduced to 70% from 90%.

R - Bonus attack range reduced 50/75/100 -> 50 all ranks

R - Void Remora health reduced 70% all ranks -> 50/60/70% max health -> 40/50/60% -> 20 /45/70%

R - Health ratio reduced 25/30/35% target's missing health ->25% all ranks

R - Bonus health bonus AD ratio reduced 165% bonus AD ->120%

R - Heal bonus AD ratio reduced 165% bonus AD -> 120%

R - Bonus movement speed 25/50/75 -> 10/45/80

V14.14

• Stats
  • Attack range reduced to 150 units from 175.
• Endless Banquet
  • Bonus attack range increased to 75 units from 50.

V14.9

• Death in Lavender
  • Bonus attack speed per Lavender stack reduced to 0.28% − 1% (based on level) from 0.28% − 1% (based on level). Now scales until level 17 instead of 13.
• Void Surge
  • AD ratio reduced to 100% AD from 110% AD.
  • Removed: No longer deals 140% damage to monsters.
  • New Effect: Now deals 45 / 55 / 65 / 75 / 85 bonus damage to monsters.

V14.5

• Death in Lavender
  • Bug Fix: Per- Voidgrub and  Rift Herald takedowns now properly grant 2 Lavender stacks instead of 3.
• Royal Maelstrom
  • Damage reduction reduced to 35 / 40 / 45 / 50 / 55% from 42 / 49 / 56 / 63 / 70%.

V13.21

• Royal Maelstrom
  • Cooldown reduced to 20 / 19 / 18 / 17 / 16 seconds from 24 / 22.5 / 21 / 19.5 / 18.

V13.20

• Death in Lavender
  • Bonus attack speed from ability casts reduced to 20% − 40% (based on level) from 25% − 50% (based on level).
• Royal Maelstrom
  • Damage reduction reduced to 42 / 49 / 56 / 63 / 70% from 70% at all ranks.
  • Minimum base damage per hit reduced to 6 / 7 / 8 / 9 / 10 from 8 / 10 / 12 / 14 / 16.
    • Maximum base damage per hit reduced to 24 / 28 / 32 / 36 / 40 from 32 / 40 / 48 / 56 / 64.
  • Minimum AD ratio per hit increased to 8% AD from 6% AD.
    • Maximum AD ratio per hit increased to 32% AD from 24% AD.
  • On-hit, on-attack, and spell modifier increased to 8% − 32% (based on target's missing health) from 6% − 24%.
  • New Effect: Damage can now critically strike.
• Endless Banquet
  • Bonus movement speed changed to 10 / 45 / 80 from 25 / 50 / 75.
  • Remora health changed to 20 / 45 / 70% of minion's maximum health from 40 / 50 / 60%.

V13.15 - August 3rd Hotfix

• Void Surge
  • Bug Fix: Directional indicators restored.

V13.13

• Endless Banquet
  • Bug Fix: No longer causes the passive mark to expire from casting  Void Surge and  Royal Maelstrom on different targets.

V13.9

• Stats
  • Attack damage growth reduced to 1.5 from 1.7.
• Void Surge
  • Damage against monsters increased to 140% from 120%.

V13.4

• Royal Maelstrom
  • Bug Fix: Initial SFX no longer improperly plays for each hit of the ability.
  • Bug Fix: Queuing the ability during  Endless Banquet no longer causes the animations for both of the abilities to stutter.

V12.21

• Royal Maelstrom
  • Cooldown increased to 24 / 22.5 / 21 / 19.5 / 18 seconds from 22 / 20.5 / 19 / 17.5 / 16.
• Endless Banquet
  • Void Remora health reduced to 40 / 50 / 60% of minion's maximum health from 50 / 60 / 70%.

V12.15

• Royal Maelstrom
  • Bug Fix: Fixed a bug where it would not cancel when casting  Endless Banquet on an out-of-range Void Coral.

V12.14

• Royal Maelstrom
  • Bug Fix: The ability will no longer globally attack the enemy  Renata Glasc while Bel'Veth is affected by  berserk.

V12.13

• General
  • Primary resource bar now tracks the remaining duration of  True Form.
    • Passive stacks are now displayed by a secondary resource indicator under the health bar.
• Endless Banquet
  • Bug Fix: Ranged Void Remora now properly receive the  Hand of Baron buff.
  • Bug Fix: Void Corals no longer spawn between the normal realm and the  Realm of Death.
  • Size while in True Form has been slightly decreased.

V12.12 - June 30th Hotfix

• Stats
  • Attack damage growth reduced to 1.7 from 2.
  • Health growth reduced to 99 from 105.
• Royal Maelstrom
  • Lifesteal reduced to 20% at all ranks from 20 / 21.5 / 23 / 24.5 / 26%.
  • Cooldown increased to 22 / 20.5 / 19 / 17.5 / 16 seconds from 22 / 20 / 18 / 16 / 14.
• Endless Banquet
  • Bonus health bonus AD ratio reduced to 120% bonus AD from 165%.
  • Heal bonus AD ratio reduced to 120% bonus AD from 165%.

V12.12

• General
  • True Form basic attack animation adjusted to swing slightly less at slower attack speeds.
  • Bug Fix: Attack SFX are no longer audible through the Fog of War occasionally.
• Stats
  • Attack range increased to 175 from 125.
  • Base health regeneration reduced to 6 from 8.5.
  • Health regeneration growth reduced to 0.6 from 0.85.
• Death in Lavender
  • New Effect: Now gains Lavender stacks from scoring takedowns against large minions on  Summoner's Rift) within 3 seconds of damaging them.
  • Bonus attack speed per Lavender stack changed to 0.28% − 1% (based on level) from 0.25% − 1.25% (based on level).
• Void Surge
  • Bug Fix:  Endless Banquet's bonus true damage on-hit is no longer doubled when applied by this ability.
  • Bug Fix: No longer triggers on-cast effects (e.g.  Sheen) for casting the ability in a direction that isn't available while other dash directions are.
• Royal Maelstrom
  • Minimum base damage per hit reduced to 8 / 10 / 12 / 14 / 16 from 8 / 11 / 14 / 17 / 20.
  • Life steal reduced to 20 / 21.5 / 23 / 24.5 / 26% from 20 / 22 / 24 / 26 / 28%.
  • Animation in  True Form while at a high attack speed has been updated.
• Endless Banquet
  • Health ratio reduced to 25% of target's missing health at all ranks from 25 / 30 / 35%.
  • Bonus attack range reduced to 50 at all ranks from 50 / 75 / 100.
  • Void Remora health reduced to 50 / 60 / 70% of minion's maximum health from 70% at all ranks.
  • Bug Fix: Bonus health is no longer lost from consuming a Void Coral while already in True Form.
  • Bug Fix: Remaining duration of buff no longer occasionally fails to refresh correctly upon consuming Void Coral.
  • Bug Fix: Remora no longer spawn a Void Coral whenever dealing damage to  Sion under the effect of  Glory in Death.